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Background: The directional discrimination is lower for painful laser heat compared to non-painful mechanical stimulation. The aim of the current study was to investigate how the directional discrimination of radiant heat stimulation depends on stimulation intensity and displacement velocity.Methods: Fifteen healthy subjects were stimulated in the right volar forearm with a CO2 laser at intensities that were expected to be either painful (46°C) or non-painful (39°C). The laser beam was continuously displaced distal-proximally along the arm during the stimulation. After the stimulation, subjects indicated the perceived direction and intensity (NRS: 0: perception 3: pain 10: maximum pain). Stimulations were delivered with five lengths (20, 40, 60, 80 and 100 mm) and three velocities (10, 30 and 100 mm/s). To estimate the directional discrimination threshold (DDT) the data were fitted to a sigmoidal curve.Results: For the lower intensity (39°C) the DDT was 81.8 mm for the slowest velocity, and above 100 mm for the two faster velocities. For the higher intensity (46°C) the DDT was 58.8 and 69.6 mm for the slowest velocity and middle velocity, respectively, and above 100 mm for the fastest velocity. The perceived intensity increased with stimulation length, stimulation intensity and decreasing velocity (LMM, p < .001).Conclusions: This study shows how the DDT for thermal stimuli is shorter for higher intensity and lower displacement velocities. Additionally, it was shown that for the velocity where directional discrimination is optimal for mechanical stimuli it is not possible to discriminate a thermal stimulus.Significance: This study showed that the directional discrimination of painful laser stimuli is better than that for non-painful laser stimuli. These findings supplements our current knowledge regarding the tempo-spatial discrimination in the nociceptive system, where evidence from previous discrimination studies differs somewhat regarding difference between painful and non-painful discrimination. This, therefore, indicates that there is lacking knowledge regarding the discrimination within the nociceptive system. [ABSTRACT FROM AUTHOR]

Background: This study aimed to explore conditioned pain modulation (CPM) effect on long-term potentiation (LTP)-like pain amplification induced by cutaneous 10-Hz conditioning electrical stimulation (CES).Methods: Conditioned pain modulation was induced by cold pressor conditioning stimulus (CPCS) (4 °C) which was applied immediately before CES in the active session. In the control session, water with a temperature of 32 °C was used. Twenty subjects participated in two sessions in a randomized crossover design with at least 1-week interval. Perceptual intensity ratings to single electrical stimulation (SES) at the conditioned skin site and to pinprick and light-stroking stimuli in the immediate vicinity of the CES electrodes were measured . Superficial blood flow (SBF), skin temperature (ST) and heat pain threshold (HPT) were measured covering both homotopic and heterotopic skin. The pain intensities during CES process were measured and short-form McGill Pain Questionnaire (SF-MPQ) was used for assessing CES pain experience.Results: Cold pressor conditioning stimulus reduced pain perception increments to weak pinprick and light-stroking stimuli after 10-Hz CES compared with the control session. Moreover, CPCS resulted in lower pain intensity ratings during CES process but without affecting the SF-MPQ scores between two sessions. The SBF and ST increased after CES and then gradually declined but without differences between CPCS and control sessions. CPM did not affect HPT and pain intensity increments to SES.Conclusions: The CPCS inhibited heterotopic perception amplification to weak mechanical stimuli after CES. The results indicate that endogenous descending inhibitory systems might play a role against development of non-nociceptive perception amplificatory states (e.g. allodynia).Significance: Conditioned pain modulation (CPM) may play a role in inhibiting the pain amplificatory process at the central nervous system and prompting central desensitization. CPM has a special inhibition effect for the development of perception amplification to non-painful mechanical stimuli. [ABSTRACT FROM AUTHOR]

Introduction Application of electrical stimulation through conventional surface electrodes activates both non-nociceptive and nociceptive fibres. To encompass this problem, electrical stimulation through small area pin electrode was introduced where subjective description of stimulation quality indicated preferential activation of nociceptors. The present study aimed to show that brain areas involved in nociceptive processing are activated by stimulation through cutaneous pin electrode ( CPE) to a larger extent than conventional surface electrodes. Methods Evoked potentials ( EPs) were induced by electrical stimulation through conventional surface and CPE electrodes. The EPs were recorded from 62 scalp electrodes in 12 healthy volunteers where stimulation intensity was 10 times the sensory threshold. Dipolar models of brain sources were built by using the brain electrical source analysis. Results The solution for the conventional large area surface electrode was a four-dipole model including contralateral primary somatosensory cortex, bilateral secondary somatosensory cortex ( SII) and mid-cingulate sources. The solution for CPE was a five-dipole model and very similar to that previously described to explain the topography of laser EPs. The solution included bilateral SII, bilateral insula and mid-cingulate sources. Since laser stimuli mainly activate nociceptive fibres, the strong similarity suggests that mainly nociceptive inputs are involved in generation of CPE-evoked responses. Conclusion The current study gives evidence that CPE activates the nociceptive brain areas to a greater extent than conventional surface electrode. Therefore, CPE should preferentially be utilized in future studies where electrical stimuli are used to study nociception. [ABSTRACT FROM AUTHOR]